Property Specification Language

Syntax and semantics

PSL can express that if some scenario happens now, then another scenario should happen some time later. For instance, the property "a request should always eventually be grant ed" can be expressed by the PSL formula:

The property "every request which is immediately followed by an ack signal, should be followed by a complete data transfer, where a complete data transfer is a sequence starting with signal start, ending with signal end in which busy holds at the meantime" can be expressed by the PSL formula:

A trace satisfying this formula is given in the figure on the right.

PSL's temporal operators can be roughly classified into LTL-style operators and regular-expression-style operators. Many PSL operators come in two versions, a strong version, indicated by an exclamation mark suffix ( ! ), and a weak version. The strong version makes eventuality requirements (i.e. require that something will hold in the future), while the weak version does not. An underscore suffix ( _ ) is used to differentiate inclusive vs. non-inclusive requirements. An a_ and e_ suffixes are used to denote universal vs. existential requirements. Exact time windows are denoted by [n] and flexible by [m..n].

SERE-style operators

The most commonly used PSL operator is the "suffix-implication" operator (a.k.a. the "triggers" operator), which is denoted by |=> . Its left operand is a PSL regular expression and its right operand is any PSL formula (be it in LTL style or regular expression style). The semantics of r|=>p is that on every time point i such that the sequence of time points up to i constitute a match to the regular expression r, the path from i+1 should satisfy the property p. This is exemplified in the figures on the right.

The regular expressions of PSL have the common operators for concatenation ( ; ), Kleene-closure ( * ), and union ( | ), as well as operator for fusion ( : ), intersection ( && ) and a weaker version ( & ), and many variations for consecutive counting [*n] and in-consecutive counting e.g. [=n] and [->n] .

The trigger operator comes in several variations, shown in the table below.

Here s and t are PSL-regular expressions, and p is a PSL formula.

Operators for concatenation, fusion, union, intersection and their variations are shown in the table below.

Here s and t are PSL regular expressions.

Operators for consecutive repetitions are shown in the table below.

Here s is a PSL regular expression.

Operators for non-consecutive repetitions are shown in the table below.

Here b is any PSL Boolean expression.

LTL-style operators

Below is a sample of some LTL-style operators of PSL.

Here p and q are any PSL formulas.

Sampling operator

Sometimes it is desirable to change the definition of the next time-point, for instance in multiply-clocked designs, or when a higher lever of abstraction is desired. The sampling operator (a.k.a. the clock operator), denoted @, is used for this purpose. The formula p @ c where p is a PSL formula and c a PSL Boolean expressions holds on a given path if p on that path projected on the cycles in which c holds, as exemplified in the figures to the right.

The first property states that "every request which is immediately followed by an ack signal, should be followed by a compete data transfer, where a complete data transfer is a sequence starting with signal start, ending with signal end in which data should hold at least 8 times:

But sometimes it is desired to consider only the cases where the above signals occur on a cycle where clk is high. This is depicted in the second figure in which although the formula

uses data[*3] and [*n] is consecutive repetition, the matching trace has 3 non-consecutive time points where data holds, but when considering only the time points where clk holds, the time points where data hold become consecutive.

The semantics of formulas with nested @ is a little subtle. The interested reader is referred to [2].

Abort operators

PSL has several operators to deal with truncated paths (finite paths that may correspond to a prefix of the computation). Truncated paths occur in bounded-model checking, due to resets and in many other scenarios. The abort operators, specify how eventualities should be dealt with when a path has been truncated. They rely on the truncated semantics proposed in [1].

Here p is any PSL formula and b is any PSL Boolean expression.

Expressive power

PSL subsumes the temporal logic LTL and extends its expressive power to that of the omega-regular languages. The augmentation in expressive power, compared to that of LTL which has the expressive power of the star-free ω-regular expressions, can be attributed to the suffix implication, a.k.a. triggers operator, denoted "|->". The formula r |-> f where r is a regular expression and f is a temporal logic formula holds on a computation w if any prefix of w matching r has a continuation satisfying f. Other non-LTL operators of PSL are the @ operator, for specifying multiply-clocked designs, the abort operators, for dealing with hardware resets, and local variables for succinctness.

Layers

PSL is defined in 4 layers: the Boolean layer, the temporal layer, the modeling layer and the verification layer.

Language compatibility

Property Specification Language can be used with multiple electronic system design languages (HDLs) such as:

When PSL is used in conjunction with one of the above HDLs, its Boolean layer uses the operators of the respective HDL.